Andrew,
The following is a copy of a Microsoft article (copied most of it):
The computer wakes when you remove a device from a computer that is running
Windows Vista.
View products that this article applies to. Article ID : 935267 Last Review
: April 3, 2007 Revision : 1.0\
SYMPTOMS
When you remove a device from a Windows Vista-based computer that is asleep,
the computer wakes. For example, the computer wakes when you remove a USB
keyboard or a USB mouse.
You may not notice when a portable computer that has its lid closed has
awakened. Therefore, battery power may be consumed.
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CAUSE
This problem occurs because the default configuration of a device in Windows
Vista lets it wake the computer.
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WORKAROUND
To work around this problem, use Device Manager to prevent the device from
waking the computer. To do this, follow these steps:1. Click Start, type
devmgmt.msc in the Start Search box, and then click devmgmt.msc in the
Programs list.
If you are prompted for an administrator password or for confirmation, type
your password, or click Continue.
2. In Device Manager, right-click the device, and then click Properties.
Note To find a USB keyboard or a USB mouse, expand Human Interface Devices.
3. Click the Power Management tab.
4. Click to clear the Allow this device to wake the computer check box.
5. Click OK.
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STATUS
Microsoft has confirmed that this is a problem in the Microsoft products
that are listed in the "Applies to" section.
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APPLIES TO
• Windows Vista Home Basic
• Windows Vista Home Premium
• Windows Vista Ultimate
• Windows Vista Business
• Windows Vista Enterprise
• Windows Vista Starter
• Windows Vista Home Basic 64-bit edition
• Windows Vista Home Premium 64-bit edition
• Windows Vista Ultimate 64-bit edition
• Windows Vista Business 64-bit edition
• Windows Vista Enterprise 64-bit edition